Automatic telephone trunking system.



W. L. CAMPBELL.

AUTOMATIC TELEPHONE TBUNKING SYSTEM.` APPLICATION FILED MAY I2, ISOB.

8 SHEETS-SHEET 2.

W'. L. CAMPBELL.

AUTOMATIC TELEPHONE TRUNKING s111511.

Patented Sept. 26, 1916.

V 's SHEETS-sain 3.

APPuc/mou man MAY x2. 190s.

,7. A, LA;

' w. L. CAMPBELL. AUTOMATIC TELEPHONE TRUNKING SYSTEM APPLICATION FILED MAY 12. i908.

Patented Sept. 26,1916.

B SHEETS-SHEET 4.

W. L. CAMPBELL. AUTOMATIC TELEPHONE TRUNKING SYSTEM.

APPucAT'loN man www12. 190s@ Patented Sept. 26, A1916.

8 SHEETS-SHEET 5.

W. L. CAMPBELL. AUTOMATIC TELEPHONE TRUNKTNG' SYSTEM.

APPLICATION FILED MAY l2. 1908. I x

Patented bept. 26, 1.916i

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N s@ i I v @25W www;

wL. CAMPBELL. AUTOMATIC TELEPHONE TRUNKiNG SYSTEM.

APPLICATmN man MAY n. 190s. 1,199,156, v Paentedept. 26,1916.

8 SHEETS-SHEET 8..

r illhlslsiel I MOR/m75 K CII ` other board, or

-When a subscriber of one ,change calls a subscriber of another divierator completes the ,with the more STATES OFFICE. WILSON L. CAMPBELL, OF LAGRANGE, To AUTOMATIC ELECTRIC CIOMPANY, OF CHICAGO, ILLINOIS, .A CORPORATION OF ILLIN'OIS.

Specification of Letters Patent.

AUTOMATIC TLEPHON E TRUNKIN G SYSTEM.v

Patented septies, 191e.

Application led May 12, 1908. Serial No. 432,551.

To all whom t may concern,"

Be it known that I, WILSON L. CAMPBELL, a citizen of the United States of America, d resident of La Grange, Cook county,

inois, have invente useful I lowing is a specification.

f y invention relates to telephone lsystems in'general, but more particularly to systems aving a divided central, or in which more than one exchange is employed, thus necessitating trunking between the boards of the same or different exchanges. In systems of ,this kind the calling subscribers line terminates at one board, or at one exchange, and the called subscribers line terminates at anat a different exchange,

division or exsion of the same system. In such caseit is usual for the operator to trunk the calling subscriber intoconnection with the lboard 0f the called subscriber, or into connection or less distant exchange of the called subscriber, and then another op'- connection with the called subscribers line.- In exchanges of this kind the different switchboards are sometimes-referred toas A and B boards, and the operators thereof as A and B operators, and it is the trunking between the A and boards, or the A and to which my invention more particularly relates. Ordinarily this trunkinglis purely manual, and is only accomplished after the originating operator-that is to say, the operator who receives the call 'from the callingl subscriberhas ascertained which of the iiferent trunks is idle and in condition to be used for ltrunking the call to the other board, or to the other exchange. arrangement requires what are ordinarily own .as order wires between the different operators, over which one operator gives the other instructions as to which' trunk is to be use etc., which arrangement and mode of operation are more or less ine`- cient, 'as considerable time'is wasted.-

e principal object of selection of trunks between the A and B boards, or between the different exchanges,

1s purely automatic, and'preferably of such i connection to a tru B operators,

y crease the v my inventiont'is, therefore, the provision of means whereby theH cally found as a result of the simple act on the part of he 'originating operator of plugging into a trunking jack-that is to say, of such character lthat the operator who receives the callfrom thecalling subscriber n eed not endeavor to ascertain which the other exchange, but into a jack and thereby nect with an idle trunk. l

t is also an object of myinvention to provide means whereby the said jacks may have signals for indicating when they are busy-that is to say, of such. character that the operator may instantly determine which jacks are in condition lfor extending it being understood that when all of the trunks which .are accessible through the medium of any particular jack are busy, a signal is then displayed at such jack, and the operator understands instantly that in order to obtain an idle trunk shev must plug into some other jack at which no signal is displayed.

In the preferred form of my invention, as herein disclosed, theauto'matic selection of trunks precedes the calls, so that when an operator plugs 'into a trunking jack, connection is immediately made ywith a trunk that h l the plugging into a .trunking )ack is followed only by ian automatic connection with the preselected idle trunk-leading to the other' board,`or to the other exchange, and t e automatic selection of another trunk forthe nextl call. y invention also consists in certain improvements in the automatic trunking switches, more especially with reference to the operating circuits forthe combined trip and release magnetsV of. 'said switches, as

v as been selected beforehand, whereby well as the locking circuits therefor, as will hereinafter more fully appear.

It is also an object of provide certain details and f provement and combination tending to ingeneral eiiiciency and serviceability of a telephone exchange -system of this particular character.

To' the foregoing and other useful ends,

eatures of imrny inventionacon'sists in mattershereinafterset forth' and Claime l In t e accompanymg drawings,

l represents'k dia'gralnmatically@anu manual my invention to Fi re' gu A110.

shaft advances eac-h time an idle trunk is P, over the line and throu seized, the plunger 13 is not advanced, but 49 to ground G1. The line remains in this position opposite the trunk and closes the circuit throu The operator then in since the slot 38 is not in engagement With into the answering Y the plunger shaft. After all of the trunkcuit is closed thro lines have-been successively seized and the said shaft 37 is released from this last position,y through the cut-o the said shaft then starts toward starting sleeve of the jack 10 and th point, or normal position, and picks up the plug p, relay 50, thence thro plunger ,13 When the web or flange of the and to ground G. said shaft-over which the slot 38 normally upon energizes and attracts 1 rides arrives at the position at which the and 49 into plunger 13 was originally released*that is, points 51 and the plunger passes into locked engagement then extended to the with the shaft. From thence on the plunstation transmitter 1S ger 13 is-carried by the shaft 37 until it is battery current from again released when another call is made.; relay 53, through th but if, after the plunger is released and bejack to the contact fore the shaft 37 'returns to pick up the transmitter 2, throu said Vphuigclgpthe switch C. is again operimpedance coil 6, ar ated, the plunger 13 again engages the Same 52, through the sleeve of the mlal Q- relay 50 and to battery B1. The master switch M, which may be of and 'thereupon energize an any suitable or approved type, is ,previded respective armatures 54 and 5 for operating the plunger shaft 37, and for The operator, u l,contro-lling certain circuits that Will be dsscriber of a distan closed hereinafter. It comprisesv the followserts the ing details: the motor magnet 39 for oper- Vhen the ating-the ratchet Wheel 40, which latter is 56 and 57 designed for operating' theplunger shaft 37 closing lan ener and a relay 41 for controlling the energizing magnet; 11 of t circuit of the motor magnet 39. The master This circuit ext switch'also has a bank O comprising a set the Springs 57 of ccntacts a and common metallic seg- 5), through the Anient 42. The Wiper 43 is adapted to remain 23, motor magn in constant engagement With'the bank O and motor maget to maintain one of the segments a in electhe winding of -trical connection with the common segment battery B, and 42. The motor magnet 39 is provided with magnet 11 ther an armature 44 -upon the end of which is ates to thrust th mounted a pawl 45. When the magnet 39 vQ, but on account o energizes, the paWl 45 operates the ratchet resistance of the ma wheel 40, thereby turning the pin 46 one rent does not flow to terminal from which it has just disengaged, 9.

notch. The pin 46, upon turn1n r eration When one subscriber calls another.

Suppose, for example, that .the subscriber at signal relay 67. substation P desires to speak with the subground G4 scriber at substation P1, the line of which conductor terminates in a second exchange. lWhen the circuitexten engagement W plug p? into t plug p1 enters the jack essed into cont gizing circuit he line switch ends from ground G3 t and 56, conductor 58 (Fi magnet 11, springs 22 and gs 59 and 60, 61 and 62, throu or magnet 39 to the ound G. The izes and oper- 3 linto the bank mparatively high gnet 11, sufficient curet relay sprin thence to gr upon energ e plunger 1 A g, bears When the plunger agalnst the cam-arm 47, which in turn moves .SPI-.in

the plunger shaft 37. and

llhe operators cord-circuit C1 (Fig. 6) engagement of the s may be any suitable cord-circuit, and thev 3l and 32 extends t gsf29 and 30, 3 35 and 36 are pre which ter 68, through battery lead 26, t nd to ground G.

. relay 67 to subscriber at substation P removes his rebattery B a ceiver from the switch-hook an energizing uponenergizingcircuit is established through the line relay which o 7, said circuit extending from battery B time. through the line relay 7, armature 48 to the bank termi line conductor, then through the substation and 36 in gh the armature relay 7 energizes gh the line lamp serts the plug p whereupon a cirugh the cut-olf relay 8. ding from ground Gr2 y 8, through the e sleeve of the ugh battery B1 li relay 8 therets armatures 48 ith the contact he subscribers lines are jack 10, and the subprovided with talking ground G through the e tip of the plug and armature 48, Y the sWitch-hook', Contact point jack and plug, The relays d attract their pon learning that a subge is Wanted, in-

jack J. the springs act, thereby through the 1g. 5). hrough enters the bank the 33 and 34', Contact. The gs 29 and 30 and conductors and 66 I circuit extends from gs 34 and v33, inding of the hence through The relay 67, rmature 69, l'ect at this` lil 4contact point 100, armature 99, through the to ground G, the relay 76 in the meantime tip of the plug p2 and jack J2, contact point remaining energized, as above explained. 93, armature 91, through the substation P1, The A operator of the cord circut C is thus armature 92, contact point 94, 'sleeve of the 'given the disconnect signal by both subjack J2 and plug p2, conductor 90, relay88, scribers P and P1, and she withdrawsthe 7o thence through battery B to ground G. The plugs p and p1 from their respective conrelay 101 thereupon energizes and attracts tacts. When the plug .p1 is withdrawn from its armature 102 from engagement with the the jack the springs 56 and 57 disengage, contact point 103 to the contact point 104. thereby breaking the energizing circuit The engagement of the armature -102 and through the magnet 11 of the line switch 'L `75 the contact point 104 provides an energizing (Fig. 5). Tlie armature 12. returns to norcircuit for the relay- 105 extending from mal position, thereby withdrawing the vplunground G1 through the armature 86, contact ger 13 from the bank terminal QI Also,

' ,Tpoint 96, armature 102, contact point 104, when the plug p1 is wthdrawnirom the relay 105, thence through battery B to jack J the energlzing circuit through the 80 ground G. i' The relay 105 thereby energizes supervisoryrelay 75 yoi" the cord circuit C1 and attracts its armature 97 from the con- (Fig. 6) is broken, and this,rela permits tact point 98 to the. contact point 106. The its armature 83 to return to norma positiondisengagement of the armature and the conin engagement with the contact point 115,v tact point 98 breaks the circuit through the thereby providing a circuit for th lamp 85, 85 supervisory lamp 95, whereupon the opersaid circuit extending from ground G" ator knows that th called subscriber has through the armature 86, contact point 96, answered. The engagementof the contact armature 1 02, contact point 103, conductor point 106 by the armature 97 provides a 116, contact point 115, armature 83, supere locking circuit for the relay 105. Furthervisory lamp 85 tothe battery B, thence to 90 more, when the relay 101 energizes, the (arground G. The glowingof the lamp at this mature 107`engages the contact point 1 08, time indicates to the B operator that the whereby a shunt is clo around the high trunk-line conductors 65 and 66 have been resistance coil 75. The relay 80 ofthe cord vacated, and she then accordingly witheircuit C now energizes and attracts its draws the plug p2 from the jack J2, thus re- 95 armature 109 from the contact point 110, storing all the central ol'iice equipment tothereby breaking a `circuit through the normal position. fj supervisory lamp 111, thus indicating to the In the foregoing it has been explained A operator that the subscriber at substation how the central oce equipment is operated 1 has answered. The two substations being to establish connection between a subscriber 100 thus connected, communication may be of one exchange and a subscriber of another carried on `over the conductors shown by exchange by means of the trunk line switch the heavy lines in Figs. 4, 5 and 6. L. It will now be pointed out from Figs. When the calling subscriber at substation 1, 2 and 3 how the trunk-lines are grouped P hangs up his receiver therelay 53 deor multiplied. As shown in Fig. 1, the dif- 105 energizes, permitting its armature 55 to fall ferent A operators positions are indicated back. The relay 50, however, remains enerat A1, A2, A3, A, etc. From each operators gized through the circuit extending from position there are trunk-lines leading to the grouiidfGf" at the cut-oii relay, as previously groups of line `switches L1, L2, L1, L4, etc'., stated. lWhen the armature 55 falls back a and from the line switch groups trunk-lines .110 circuit is'provided for the supervisory lamp lead to the B operators. The A1 position 112, giving the operator the disconnect-sigwill be considered. From thejack J atrunknal so far as the subscriber P is concerned. e line leads to a line switch in the group L1' Now, when the subscriber at substation P1 from the second jack J a. trunk-line lends restores his receiver the energizing circuitto a line switch in the group L2; and @om 115 through the relay 101 of the cord-circuit C1 is the third jack J a third trunk-line leads to broken, permitting the armatures 107 and a line switch in the group L, ctc. From the 102 to return to normal position. When the remaining positions A2, A2, A, etc., there is armature 107 disengages from the contact a trunk-line to a line switch in each one of point 108 the high resistance relay, 75 is the groups L1, L2, L2, etc., there being'as 120 placed in a series circuit with the relays 8O many trunk-lines from each position as there and 76 of the cord circuit C. As previously are groups L1, L2, L2, etc. This is one arexplained, when the relay 80 is in series withl rangement. Sometimes it may be advanthe high resistance coil 75 it permits its tageous to provide a plurality of trunk lines armature 109 to fall back to normal position, leading' from one operators position to a 125 whereby an energizing `circuit is established plurality of line switches. The line switches through the lamp 111. This circuit extends may be distributed into one or more groups, from ground through the armature 109, consuch as groups L1, L2, etc. By 4means of the tact point 110, armature 113, contact point slip multiple arrangement shown in Fig. 2

' 114 and lamp 111 to the battery B, thence the remaining operators positions lof the @im trihuted among theV B operators.

manual hoard muy he connected with any lineswiteh which is accessible 4to any other position.

In Fig.

the 2 position leeds to n'line 'L1 group, und the lust jack in theA A@ posi- `tion lends to n line switch in theV L group.

From each group U, L2, L, etc., there muy he ten trunk-lines lendingl to the i3 operators. Thus, in either of the above errunge- Y. ments, since each A operatorhas access to ull of thegroups L1, L2, L, ete., all of the trunks to the v"B operators ure vaccessible` from any A operutors position. y y 'in Fig. 3 is shown how the trunks from the diiiei'entgroups L?, L2, L3, etc., `are dis- .FOI' ille.. stunee, the ten trunks from the' group L1.- :ue distributed as follows: Afour to the -B position, three to theB2 positionfend `three to theB3 position. `The trunks from the group LL Aare divided among the three posi., tions in n similarinunner. Another ar. rangement, hnwerer, may he resorted to.

Referring to Fig. 5, 1t was shown hoiV,

when the line switch L .operated to. seize u truuk-line, un energizing circuit vvns estaba. lished through the relay G7., Suppose, now, that :t second lineA switehin the sume .group operates to seize-u second trunk, and-.so on through the third, fourth and, fifth,- until all the trunk-lines in; the/L1 group are seized, all theflelays'', 67,1 67, G7, etc.,L

' hecoine energized, attr-noting theirrespectivey armatures.

lines of this group are lousy.

A tion of Fig. 5- in which the outside` springs of e ground .Gr-1 not When ull these reluysure thus? energized n. ,circuit is established extending. from ground (lm through v euch Vsuccessive contact point und armature of `the .ten ref lays ullottedgtothe ten trunk-lines, through the conductor 117, then through' lthe .lamps S1, S?, S, S4, ete., one of which .is allotted' toleech A operutors 1 )osition A1, A2, A3, A4, etc.,.in front of the jack ofA the trunk-line 'which leads to this group L1, therebyindi-| eating'to the operators that all of the trunkstated, is a 'modiicaf the Work done luythe relays 67, 6T, (37b, 'ic, etc., isdone lin the hunk termina-ls Q, QLQ, Qayetc., when thev plunger is operated-thet is, 1 when the plunger 13 is thrust intov the terminulrhunkv Q the springs' and 34: are-pre'ssedfinto Contact.Y .NVhen the next terminal isseized f the terminal iQ? :rre-` pressed into Contact, and so. on When'Q, QH' etc., are" seized. The final connection vwitlry being `established until the Fig 7, as previously naisy Q1, Q2, Q3,- etc.,

last terminal QP is seized, then the ground G19. is transmittedthrough all of the termi beek to the relay 118, thneeto the battery leed 26, and through buttery B to ground G. The. relay 118 then .operates to pressthe springs 119l und 1520 into eontect, whereby n. circuit is closed through ,the signal lamps S1, S2, S3, ete.,

said cirouit `extending from ground G1 through the springs 120 und 119, lumps S1, S?, S3., etc., in multiple to the buttery leed 26,;thence through battery B to ground G. 1n Fig. 8 the cord-circuit C is e modified 'form of the cord-circuit C The trunk line switch' L (Fig. {i} is con` Y trolled from the jack .l (Figs. e and S) over ,the conductor 58.4 Referring to Fig. el it ,Will he seen that the trunk line switch is tripped in es Soon as the plug p1 enters the jaclcJ und presses the springs 'and 5T `into Contact, therehytrensinitting e ground tothe conductor 58 and energizing the trip magnet 11. lThe trunk line switch L re- ,-nmins in an operated position long es the ,plug p1, remains in t .e inch and maintains the ground eonneetiu to the Conductor 58. In Fig. 8 the ground 'honneetion to the oon- .ductor. is controlled from one of the supervisory relays of the cordcirouit. is so urrungedthut when the plug p1 enters lthe jack J, ground for operating the line switch L is transmitted from ground G through the eontuct `point 5T, armature 5G ofthe vulling suhscribers Supervisory relay to the conductor switch L (Fig.`5).1 Furtherrnor Calling subscriber restores his receiver to the Aswitclnhook,` the relay 58 denergizes, and the armature 56 felis away from the ground rontuct point 57, thereby removing ground from thev conductor y58 und permitting the vtrunk line switeh L to 'restore itself to non :nmlposition even before the operator removes the' plug from the jack. The calling s ,uhscriherv therefore `controls the clearing out and makes the trunk to the B-hoard-dle v,its soon ashe restores his receiver. 1n draw ings',fus shown in Fig. 4, the trunk to the B-hourd is notinade idle until' the A opera- When `the tori removes the' 'plug from the line switch jack. 1 Y

From the foregoing it Will trunking between the A and'B boards of the sameJ exchange, or between the-A and B op? erators of different vexchanges in. thefsame system, isentirely Ytult'om'zitic, end ith'et the operators are not'required to asoert"y trunks ure lidle und l'n condition `fo use, `us vthe 'mere :1ct of-y plugging intov ani idle trunk jack f l n is suflioien't'to autoinutiee i --tend the 'curl-ling fsuhseribers line leadlngto tne nection with un' idle ltrunk V'other hoard, or to the other exchange. 1f the 'A-hourd. for exur'nple," 'has several sectionsQl ,il n. vthen fthere muy he as 'runny trunk Jucksln lThis he seen that the 58 which leads to the line 100 vhich -are busy, and that some other or B boards, different exchanges, in the same system, are a common to each and every section into Which suchboards may be divided, although if it requires more than one operator to a secset of trunks. The signals provided and associated with the trunk jacks indicate to the .operatorsthe condition of such jacks, showl lngwheth'er the same are available for obtaining access to an idle trunk. If a signal is displayed at a trunk jack, then the operator understands that all of the trunks to which: access is afforded through this jack idle jack must be used in extending the call over an idle trunkA to the other board. The idle trunks are preselected, so that when an operator plugs into a trunk jack the only result that follows therefrom is the automatic connection of the jack with a preselected idle trunk, and the automatic selection of another trunk for the next call. Thus', each time that an operator plugs into a jack two things happen, namely the automatic connection of that Jack with the preselected idle next idle'trunk, which newly selected idle trunk will be given the next operator who as occasion to make a trunk connection. Furthermore, it will be seen thatwith the system of slipping or cross-multipling employed, such as shown in Fig. 2, the multiple jacks allotted to any particular' trunk leading to an automatic trunkingswitch do not occupy like or similar positions in the different operators positions, wherebydiiierent operators each have their vmultiple jacks differently arranged. In this way the different operators can all plug into the first jack and obtain connection with vas `many different trunking switches, thus distribut ing the load or trafiic morer evenly between the different trunks, and preventing more wear and tear on one switch 4than others. In other words, and without such arrangement, it will be seen that the natural inclination of the operators to always plug` into the rst jack, if the same be idle, would tendto impose a great deal of work on one particular autoinati"switching machina-caving the otlirsfrratleast some of them, more or less idle agdd share of the time.

at lIfclaim as my invention is:

l. In-a telephone system, a set of trunks each terminating at one end. ina plug, an

automatioftrunk selector, a jack coniiected `cessible theref with said trunk selector, a second plug, and means operated by the insertion of said seclug into said jack for causing said selector to seize an idle trunk, and to select another trunk for the next call..

In a telephone system, a set of trunks, a" cord-circu1t plug, means for switch, means for preselecting an idle trunk, anq a ord-circuit plug, said switch comprising said plug into said jack for automaticallj7 connecting the latter with an idle preselectedY trunk.

5. In a telephone system, a set of trunk jacks, a plurality of trunks, means responsive to the insertion oi' a plug in said jacks .for automatically connecting the latter with being accessible through tbe medium of any one Jack, signals associated with said jacks,

and means for automatically displaying the signal of a jack when all of the trunks acrom are in use.

6. In a telephone exchange system, an A- board, a B-board, manual equipment on said boards, trunks between the two boards, means for automatically selecting idle trunks between said boards ahead of the call, and a line switch common to and adapted to connect with a plurality of said trunks. Y

7,. In a telephone exchange system', -a manual exchange, another exchange, trunk lines extending fromoner exchange to the other.

cally selecting idle trunk lines ahead of the call, and a line switch .common to and adapted to connect with a plurality of said trunks.

8. In a telephone system, a set of trunks each terminating in a plug, means for preselecting an idle trunk, an automatic switch for connecting with idle preselected trunks, said switch provided with an operating magnet, a trunk jack connected with said switch, a second plug, and means whereby the said magnet is energized when said second plug is inserted in said jack, and deenergized when the said plug is withdrawn therefrom,

9. In ahtelephone system, a set of trunks,

eans responsive to' the insertion of leading to the B-board, said Ameans including a line switch adapted to connect with an idle trunk extending to the B-opcrators board, said means comprising a circuit closer for performing the connecting operation, an electromagnetic release mechanism -controlled over the established connection for withdrawing the circuit closer from the bank, and moving the circuit closer, and being adapted when released to disengage from said reach a released position.

scribers lines, an A-board and a B-board for connecting said lines, trunk lines extending between said boards, automatic switches for selectingan idle trunk, trunks extending' from the Aboard to said automaticswitches, said last-mentioned trunks including a pair oi' talking' conductors and a third conductor, means for controlling the operation of said switches from the Abboard, and means controlled over one of said lines for releasing said switches over third conductor.

29,.'In a telephone system, scribers lines, an .f1-board and a B-board for connecting said-lines, trunk lines extending between said boards, automatic switches for selecting an idle trunk, trunks extending from the Aboard to said automatic switches, said lastmentioned trunks including a pair of talking' conductors and a third conductor, and means for controlling the operation and release of said switches over said lastmentioned trunks, said means ccntrolleiil over one of said lines.

23. In a telephone system, a subscribers line, an ,Ai-operators cord circuit adapted Y to be connected with said line, a .l-operators cord circuit, automatic switches controlled from the A-operators cord circuit for selecting an idle B-operator`s cord circuit,v and means controlled by the calling subscriber i'or releasing said automatic switches,

121i. In a telephone system, a subscrihers line, an A-opei'atoi"s cord circuit adapted to 4 be connected withsaid line, a Boperators cord circuit, automatic switches controlled from the Acperators cord circuit for selecting an idle lcperators cord circuit, and means controlled by the calling sul"- scriher for closing a ground connection. to the releas of said automatic a pair of suhcontrol switches.

25. In a telephone system, an A-operato1"s hoard, a B-operators hoard', a calling subscribers line terminating in said fle-opera tors board, trunks extending to the Beeperators hoard, an automatic switch, ifor leeting an idle trunk, an auxiiiary conduct associated with said trunk and exten'l from said ri-operator@ hoard to s; tic switch, a circuit iler conne aisance means for thereafter furtherv trunk without passing over other trunks to 2l. In a telephone system, a pairof subline and the trunk, and. means controlled by the calling subscriber for closing a ground connection over said auxiliary conductor-to control the release of said switch. 26. ln a telephone system, an ric-operators board, a B-operators board, trunks` terminating each in a jack in the Appelators hoard`r a. progressively movable switch for each trunk, other trunks terminating in contacts in said switches and each terminating in a plug in the B-operators board, said switches controlled by' master switch mechanism, each switch responsive to the inser tion of a plug in its corresponding jack in the A board to connect the trunk terminat-ing in said jack with one of the said other trunks terminating in the B board.

27. ln a telephone system, an A-operators board, a B-operators' board, a calling subscribers line terminating in said Abperators board, trunks extending to the B- operators board7 an automatic switch for selecting an idle trunk', another trunk extending from the ebperators board to said automatic switch, an auxiliary conductor associated with said other trunk and extending from said A-operators board to said automatic switch, a circuit for connecting the line and the said other trunk, and means. controlled by the calling subscriber for closing a circuit lover said auxiliaryconductor to control the release of said switchn 2S. In a telephone system, an 5L-operators board, a B-operators board, a plurality of lines extending to saidAL-looard7 otherA lines extending .from said board, automatic switches for said other lines, circuits for.. connecting any one of said irst lines with any one of said other lines, automatic electromagnetically controlled apparatus for controllingone of said automatic switches to extend a connection from one of said other lines to the B-operator, an auxiliary conductor associated with said connection, a relay controlled over the first line in the Connection for closing a circuit over said conductor to control the release off said switch, and a release magnet for releasing,r said switch.

29. In a telephone system, an A-board, a B-board, a plurality of lines extending to said A-board, other lines extending from said hoard, an automatic switch for each one of said. other lines, a circuit for connecting any one of said first lines with any one oi said other lines and with the automatic switch associated therewith, an operating magnet for said automatic switch controlled over the said. connecting circ-uit forextending a connection from one of said other lines to the B-operators board, an auxiliary conductor associated with said established circuit, relay controlled vover the iirst line in the connection for closing a circuit .over said eilfleator to control the release of said switch by breaking the circuit of said. operating; magnet.

30. ln a telephone system, a set of trunks each terminating at one end in a plug, an automatic trunk selector, a jack connected with said trunk selector, a second plug, means operated by the insertion of said second plug into saidl jack i'or causing said selector to seize an idle trunk and to select another trunk for the next call, said .means also responsive to the Withdrawal of said plugtor releasing purposes.

3l. In a. telephone system, a set of trunks, al trunk ack,` a cord-circuit plug, means for preselecting,r an idle trunk, and means common to a plurality of said trunks responsive to the insel' ion ot said plug into said jack for automatically connecting the latter with ail-idle preselected trunk, said means also responsive tothe Withdrawal of said plug for releasing purposes.

32. ln a telephone system, a set of trunks, means for automatically selecting idle trunks ahead of the calls, a trunk jack, and means common to a plurality of said trunks responsive to the insertion of a plug .in said jack for automatically connecting the latter `with the preselected 4idle trunk, said means also responsire to the withdrawal ot' said plug: for releasing purposes.

33. ln a telephone system, a trunk jack, an automatic switchh individual thereto, a

`set ot' trunks leading from said automatic switch, means for preselccting an idle trunk, a cord.-circuit plug, said switch comprising means responsive to the iiisertion of said plug into said jack for automatically connecting the latter 'with un idle preselected trunk, said sis'itcli means also responsive to the witlnlraufai of said plug for releasing purposes.

Si. ln a telephone exchange system, an ,AL-board, a B-board, manual equipment on said boards conmrising plugs and jacks on the ifi-board, trunks between the two boards, means for automatically selecting 'idle trunks between said boards ahead ot the call, and a line switch common to said trunks haring?, automatic .means controlled by said plugs and jacks to establish a connection with one` oi said trunks, said means also controlled-by said plugs and jacks to rclcase the comiection.

ln a telephone exchange system, a manual exchange comprising plugs and Yswitches over said meeste 3G. In a telephone` system.. originating` and trunking operators cord circuitsa set oi primary trunks and a set ot secondary trunks extending; between the two, means v operated upon the connection-oi a` cord circuit with a primary trunk hnci to' automati-A cally select an idle secondary trunk for the to the pur.

next call said means also-responsive withdrawal of said plug,` for releasing,I

poses.

3T. ln a telephone system, a callingr subscribers line and a callcd subscribcfs line, moans for connecting said lines, said means comprising an A-board and a l-boariktrunk lines extending between said boards, automatic switches for selectingl an idle trunk, trunks extending,` from the bboard to` said automatic switches, said last mentioned trunks including' a pair of talking. conduc tmfs'and a third conductor, means tor controlling the operation of said switches at the fla-board, and means controlled over the calling line for releasing said switches over said third conductor.

3S. In a telephone system, a calling' subscriber-s line and a called subscriber-s lino, means for connecting" said lines7 said means comprising an .i-board and a l-board, trunk lines extending' between said board, automatic switches for selec-tins an idle trunk, trunks extendingY 'from thc -board to said automatic switches. said lust mentioned trunks includiim a pair of talking conductors und a third conductor. and moans 'for controlling the operation and relaas(l oi said last nnntionod trunks, said last moans cont-rolled over the callilmT subsi'zribei"s line.

Signed by me at Chicago. Cook lllinois, this 30 day ot' April. WOS.

c1 n i nty,

lVituesses Haunin'r'r M. Mannini', Eowann D. Flims. 

